Due to worldwide CO2 restrictions and fuel efficiency regulations, improvement in fuel efficiency and the development of eco-friendly vehicles have been key items in automotive industry. Thus, leading vehicle manufacturers have invested heavily in developing technologies to achieve these objectives.
In a cold condition, at the beginning of starting a vehicle, an engine has low fuel efficiency in comparison with a sufficiently warmed-up engine. In a cold condition, the viscosity of oil becomes higher due to low temperature of the oil, and friction in the engine is large due to the high viscosity of the oil. Due to the low temperature of cylinder walls, heat loss through the walls is huge and the stability of combustion is deficient, and thus fuel efficiency is decreased.
Therefore, it is required to rapidly increase the temperature of the engine to a normal temperature at the beginning of starting the vehicle engine so as to enhance fuel efficiency and engine durability thereof.
In addition, recently, a hybrid vehicle has EV mode where the engine is turned off, and such a mode requires that a technology of rapidly warming up the engine when the engine is turned on during running the hybrid vehicle in EV mode.
Thus, recently, a technology of warming up coolant of the engine by using an exhaust gas temperature has been proposed.
The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art.